Departamento de Ecología, Pontificia Universidad Católica de Chile, Santiago, Chile.
Laboratorio de Paleoecología, Facultad de Ciencias Biológicas, Universidad de Chile, Santiago, Chile.
PLoS One. 2019 Jan 30;14(1):e0210369. doi: 10.1371/journal.pone.0210369. eCollection 2019.
The evolution of maize (Zea mays L.) is highly controversial given the discrepancies related to the phenotypic and genetic changes suffered by the species, the incidence of human groups and the times in which these changes occurred. Also, morphological and genetic traits of crops are difficult to evaluate in the absence of fossils macro-botanical remains. In contrast in the Tarapacá region (18-21° S), Atacama Desert of Chile, prehispanic settlements (ca. 2500-400 yr BP) displayed extensive maize agriculture. The presence of archaeological macro-botanical remains of maize provided a unique opportunity to study the evolution of this crop, covering a temporal sequence of at least 2000 years. Thus, in this study, we ask how the morphological and genetic diversity of maize has varied since its introduction during prehispanic times in the Tarapacá region. To answer this, we measured and compared morphological traits of size and shape between archaeological cobs and kernels and 95 ears from landraces. To established genetic diversity eight microsatellite markers (SSR) were analyzed in archaeological and modern kernels. Genetic diversity was estimated by allelic frequency rates, the average number of alleles per locus, observed heterozygosity (Ho) and expected heterozygosity (He). Differences between populations and genetic structure were estimated by fixation index FST and STRUCTURE analysis. Our results indicate significant phenotypic differences and genetic distance between archaeological maize and landraces. This result is suggestive of an introduction of new varieties or drastic selective changes in modern times in Tarapacá. Additionally, archaeological maize shows a low genetic diversity and a progressive increase in the size of ears and kernels. These results suggest a human selection during prehispanic times and establish that prehispanic farmers played an important role in maize development. They also provide new clues for understanding the evolutionary history of maize in hyperarid conditions.
玉米（Zea mays L.）的进化备受争议，原因是该物种经历了表型和遗传变化，涉及到人类群体的出现和这些变化发生的时间。此外，在缺乏宏观植物化石遗骸的情况下，作物的形态和遗传特征很难评估。相比之下，在智利的阿塔卡马沙漠的塔拉帕卡地区（18-21° S），前西班牙裔定居点（约公元前 2500-400 年）展示了广泛的玉米农业。考古学上发现的玉米宏观植物遗骸为研究该作物的进化提供了一个独特的机会，涵盖了至少 2000 年的时间序列。因此，在这项研究中，我们想知道自前西班牙时期在塔拉帕卡地区引入以来，玉米的形态和遗传多样性是如何变化的。为了回答这个问题，我们测量并比较了考古玉米穗和玉米粒以及 95 个地方品种穗的大小和形状的形态特征。为了建立遗传多样性，我们分析了 8 个微卫星标记（SSR）在考古和现代玉米中的等位基因频率、每个位点的平均等位基因数、观察杂合度（Ho）和预期杂合度（He）。通过固定指数 FST 和 STRUCTURE 分析估计群体间和遗传结构的差异。我们的结果表明，考古玉米与地方品种之间存在显著的表型差异和遗传距离。这一结果表明，在现代时期，塔拉拉帕卡地区可能引入了新的品种或发生了剧烈的选择性变化。此外，考古玉米的遗传多样性较低，穗和玉米粒的大小逐渐增大。这些结果表明，在前西班牙时期，人类对玉米进行了选择，并确立了前西班牙农民在玉米发展中的重要作用。它们还为理解玉米在极度干旱条件下的进化历史提供了新的线索。
